The following is an instructable on making a wooden ring out of teak at Techshop RDU. These rings can be made out of any hardwood, but teak is both water resistant and strong enough to remain intact, even with a slender profile.
Take a look at the Etsy.com website I just put up:
1) Even out the thickness of the ring on all sides. It doesn't have to be exact, as you'll come back later, but the closer you get it here the less hand sanding you have to do.
2) Tilt the ring slightly to the side, first one way and then the other, in order to round the edges off. After this step it'll begin to look less like a scrap piece and more like an actual ring. The rounding allows to to taper the profile while maintaining most of the rings structrual stability.